1. Field of the Invention
The present invention relates to an external circulation type ball screw, and more particularly to a tangent external circulation type ball screw.
2. Description of the Prior Art
Nowadays, ball screw is used more and more in the field of industry, in addition to the effect of high precision, the ball screw also has low friction, low noise and hard to destroy. Therefore, the ball screw is very important in terms of various machines.
In order to make the nut move relative to the screw endlessly, a return device must be mounted on the ball screw, such that the rolling elements can be circulated in the rolling groove endlessly. However, a return path of a conventional return device disclosed in U.S. Pat. No. 3,661,030 has a bent portion, when the rolling elements move at a high speed to impact the nail and the bent portion continually, the strength of the nail and the bent portion will be weakened. Thereby, the impact-caused scraps of the return member will fall between the rolling elements and affect the circulation of the rolling elements. Obviously, the damage of the return device will cause the failure of the ball screw.
Therefore, to solve the above-mentioned problem, a current method is to insert the bent pipe into the threaded tracks along the direction of tangent thereof, for example:
A return deice disclosed in U.S. Pat. No. 3,971,264 comprises a multi-sectional bent pipe which is a unstable structure due to it has multiple sections, and the direction of the pipe hole of the nut is the same as that of the lead-angle. Therefore, such a pipe hole is hard to process because it needs a multi-spindle processing machine.
The bent pipe of the return device disclosed in U.S. Pat. No. 4,953,419 is defined with two bent guiding passages, so the size of such bent portions is hard to control during manufacturing process. In addition, the problem of processing the pipe hole of such nut is the same as that of the above-mentioned return device. And the return device is fixed by a fixing piece mounted on the outer diameter of the nut, the return device fixed by such a method is unstable and increases the size of the outer diameter of the nut.
A return device disclosed in US Pat No. 2003/0213323 comprises plural members which are manufactured by many different molds. Thereby, the cost and the assembly time of the return device are increased, and the plural members will vibrate and cause noise when the rolling elements inside the return device move at a high speed.
In addition, the above-mentioned three conventional external circulation return devices has the same problem, that is, the position of the return device relative to the nut is hard to control, and the rolling elements are easy to fall off during the rolling-elements-loading process.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.